Impedance matching

ABSTRACT

A circuit device includes a directional coupler with a first port receiving a radiofrequency signal, a second port outputting a signal in response to signal received by the first port, and a third port outputting a signal in response to a reflection of the signal at the second port. An impedance matching network is connected between the second port and an antenna. The impedance matching network includes fixed inductive and capacitive components and a single variable inductive or capacitive component. A diode coupled to the third port of the coupler generates a voltage at a measurement terminal which is processed in order to select and set the inductance or capacitance value of the variable inductive or capacitive component.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of United States Application for patentSer. No. 17/321,757, filed May 17, 2021, which claims the prioritybenefit of French Application for Patent No. 2005058, filed on May 19,2020, the contents of which are hereby incorporated by reference intheir entireties to the maximum extent allowable by law.

TECHNICAL FIELD

The present disclosure generally relates to electronic circuits, andmore particularly to circuits comprising an antenna to transmitradiofrequency signals.

BACKGROUND

It is known to match the impedance of a radiofrequency antenna intendedto transmit a radiofrequency signal with that of a radiofrequency sourcesupplying the radiofrequency signal to be transmitted. In particular,known devices enable to match the impedance of an antenna with that ofthe radiofrequency source when the antenna is placed in its environmentof use and that this environment causes an impedance mismatch betweenthe radiofrequency source and the antenna.

However, such known devices suffer from various disadvantages.

There is a need to overcome all or part of the disadvantages of thepreviously-mentioned known impedance matching devices.

SUMMARY

One embodiment provides a device comprising: an antenna; a directionalcoupler comprising a first port configured to be connected to a sourceof a radiofrequency signal, a second port having a signal received bythe first port transmitted towards it, and a third port having a signalreceived by the second port transmitted towards it; an impedancematching network comprising inductive and/or capacitive components offixed value and a single inductive or capacitive value of settablevalue, an input terminal of the network being coupled to the second portof the coupler and an output terminal of the network being coupled tothe antenna; and a diode coupling the third port of the coupler to ameasurement terminal of the device configured to be connected to ananalog-to-digital converter.

According to one embodiment, the matching impedance network is thesingle impedance matching network of the device.

According to one embodiment, the device further comprises a low-passfilter connected to the measurement terminal.

According to one embodiment, the component of settable value is acapacitor.

According to one embodiment, the matching impedance network comprises: afirst capacitive component connected between input terminal of thenetwork and a node configured to receive a reference potential; a firstinductive component and a second capacitive component series connectedbetween said input terminal and the output terminal of the network; asecond inductive component connected between said output terminal andsaid node; and the component of settable value connected between saidoutput terminal and said node.

According to one embodiment, values of the components of fixed value aredetermined so that the normalized impedance of the device after animpedance mismatch caused by a conductive element disposed close to thedevice belongs, in a Smith chart, to an area determined by all thevalues of the component of settable value.

One embodiment provides an electronic system comprising the describeddevice.

According to one embodiment, the electronic system further comprises asource of a radiofrequency signal connected to the first port of thecoupler of the device, and an analog to digital converter connected tothe measurement terminal of the device.

According to one embodiment, the electronic system comprises amicrocontroller comprising the analog to digital converter, a digital toanalog converter controlling the component of settable value and aprocessor configured to receive measurements from the analog to digitalconverter and to provide a control signal to the digital to analogconverter.

One embodiment provides a method of use of the described device orsystem, comprising the following successive steps: a) selecting aninitial value of the component of settable value and measuring a voltageon the measurement terminal; and b) changing the value of the componentof settable value in a determined scanning direction then measuring thevoltage of the measurement terminal, step b) being repeated until thelast measured voltage is strictly greater than the penultimate measuredvoltage.

According to one embodiment, step b) is followed by a step c)determining a set comprising each value of the component of settablevalue corresponding to a minimal voltage measurement, and controllingthe component of settable value so that its value belongs to said set.

According to one embodiment, the component of settable value iscontrolled so that its value is a median value of said set.

According to one embodiment, the method comprises, previous to step a),a step of determining values of the components of fixed value of thenetwork so that the normalized impedance of the device after animpedance mismatch caused by a conductive element disposed close to thedevice belongs, in a Smith chart, to an area determined by all thevalues of the component of settable value.

According to one embodiment, determining values of the components offixed value comprises the following successive steps: 1) selectingvalues of the components of the network for which the impedance of thedevice matches that of the source of the radiofrequency signal in ananechoic environment; 2) calculating a normalized impedance of devicefor each value of the component of settable value; 3) disposing aconductive element close to the device and calculate a normalizedimpedance of the device; and 4) repeating step 2) and 3) with modifyingat least one of the values selected at step 1) and/or those of thecomponent of the network which has a settable value as long as thenormalized impedance calculated at step 3) is outside a set comprisingall the normalized impedance calculated at step 2).

According to one embodiment, steps a), b) and c) are implemented in aperiodic manner and/or on request from a user.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages, as well as others, will bedescribed in detail in the following description of specific embodimentsgiven by way of illustration and not limitation with reference to theaccompanying drawings, in which:

FIG. 1 shows, in the form of a circuit, an example of an impedancematching device;

FIG. 2 shows, in a Smith chart, impedance shifts that the device of FIG.1 is capable of correcting;

FIG. 3 shows in the form of a circuit an embodiment of an impedancematching device;

FIG. 4 illustrates, in the form of a flowchart, an implementation modeof a method of use of the device of FIG. 3 ;

FIG. 5 illustrates an implementation example of the method of FIG. 4 ;

FIG. 6 illustrates another implementation example of the method of FIG.4 ; and

FIG. 7 illustrates yet another implementation example of the method ofFIG. 4 .

DETAILED DESCRIPTION

Like features have been designated by like references in the variousfigures. In particular, the structural and/or functional features thatare common among the various embodiments may have the same referencesand may dispose identical structural, dimensional and materialproperties.

For the sake of clarity, only the steps and elements that are useful foran understanding of the embodiments described herein have beenillustrated and described in detail. In particular, the differentcircuits, for example, integrated, capable of being used as a source ofa radiofrequency signal for an impedance matching device connected to anantenna, have not been described, the described embodiments and variantsbeing compatible with usual sources of a radiofrequency signal.

In the following description, a signal is called radiofrequency (RF),for example, when the fundamental frequency of the signal is in therange from 3 kHz to 300 GHz, preferably from 100 MHz to 30 GHz. In therest of the description, a so-called sub-gigahertz or sub-GHz RF signalis more particularly considered, that is, a radiofrequency signal havingits fundamental frequency for example in the range from 400 MHz to 950MHz, although the embodiments and variants which will be described moregenerally apply to all radiofrequency signals.

In the following description, a first value is said to be smaller,respectively greater, than a second value if the first value is smallerthan or equal to, respectively greater than or equal to, the secondvalue. In addition, a first value is said to be strictly smaller,respectively strictly greater, than a second value if the first value issmaller than and different from, respectively, greater than anddifferent from, the second value.

Unless indicated otherwise, when reference is made to two elementsconnected together, this signifies a direct connection without anyintermediate elements other than conductors, and when reference is madeto two elements coupled together, this signifies that these two elementscan be connected or they can be coupled via one or more other elements.

In the following disclosure, unless indicated otherwise, when referenceis made to absolute positional qualifiers, such as the terms “front”,“back”, “top”, “bottom”, “left”, “right”, etc., or to relativepositional qualifiers, such as the terms “above”, “below”, “higher”,“lower”, etc., or to qualifiers of orientation, such as “horizontal”,“vertical”, etc., reference is made to the orientation shown in thefigures.

Unless specified otherwise, the expressions “around”, “approximately”,“substantially” and “in the order of” signify within 10%, and preferablywithin 5%.

FIG. 1 shows in the form of a circuit an example of an impedancematching circuit device 1.

Device 1 comprises an antenna 2 and an input terminal 100, having animpedance matching network 3 connected therebetween. Terminal 100 isconfigured to be connected to a source (not shown) of a sub-GHz RFsignal intended to be transmitted by antenna 2. The source of thesub-GHz RF signal is, for example, an integrated circuit (not shown)having an output terminal configured to deliver the sub-GHz RF signal tobe transmitted, this output terminal being then connected to terminal100.

Network 3 comprises capacitive components and/or inductive componentsor, in other words, comprises at least one inductive component and/or atleast one capacitive component. The inductive and/or capacitivecomponents of network 3 are coupled together and to a node 102 ofapplication of a reference potential, typically ground GND. Theinductive and/or capacitive components of network 3 couple an inputterminal 301 of network 3 to an output terminal 302 of network 3.Terminals 301 and 302 are respectively connected to terminal 100 and toantenna 2. At least two inductive and/or capacitive components ofnetwork 3 have a settable value, that is, a controlled value. In otherwords, those components are variable components.

In the example of FIG. 1 , network 3 more particularly comprises avariable capacitor C1 of settable capacitance value connected betweenterminal 301 and node 102, a fixed inductor L1 of fixed inductance valueand a variable capacitor C2 of settable capacitance value seriesconnected between terminals 301 and 302, the inductor L1 being connectedto terminal 301, and a fixed inductor L2 of fixed inductance value and avariable capacitor C3 of settable capacitance value connected inparallel between terminal 302 and node 102.

When the terminal 100 of device 1 is connected to a radiofrequencysource (not shown) of a sub-GHz RF signal, the capacitance values ofvariable capacitors C1, C2, and C3 of network 3 are modified during animpedance matching phase so that the impedance seen by the sub-GHz RFsignal on terminal 100 is equal or substantially equal to the conjugatedimpedance of the source of the sub-GHz RF signal. More exactly, thecapacitance values of variable capacitors C1, C2, and C3 are modified sothat the power of the sub-GHz RF signal which is reflected by device 1towards terminal 100 is as low as possible for the considered network 3.In other words, the capacitance values of variable capacitors C1, C2,and C3 are modified so that the impedance of device 1 is matched withthat of the source of the sub-GHz RF signal.

For this purpose, device 1 is associated with a detector (not shown)configured to provide a measurement representative of the power of thesignal reflected towards terminal 100, that is, representative of thepower of a portion of the sub-GHz RF signal supplied to terminal 100towards antenna 2 which is reflected towards terminal 100. The detectorshould be sufficiently sensitive to measure the power of the reflectedsignal, or reflected power, when the impedance of device 1 is matchedwith that of the source and the reflected power is minimal.

Such a detector, typically a logarithmic detector, is complex and costlyto implement. It would thus be desirable to be able to implement animpedance matching phase with a simpler detector.

It is here considered that the impedance of device 1 is initiallymatched with the one of the source of the sub-GHz RF signal and that theimpedance of device 1 is modified because of the environment where thedevice 1 is disposed. As a result, the impedance of device 1 has amismatch with that of the source. To suppress such an impedancemismatch, an impedance matching phase is then implemented in situ, thatis, in the environment of use of device 1.

During this impedance matching phase, since network 3 comprises at leasttwo variable components of settable (capacitance and/or inductance)value, the reflected power exhibits a plurality of local minimum valueswhen the values of the components are varied, each local minimumcorresponding to a different association or combination of values of thevariable components of settable value. As a result, the implementationof an impedance matching phase requires trying a very large number ofcombinations of values of the variable components of settable value tofind the minimum reflected power, that is, that of the local minimumvalues corresponding to the lowest reflected power. The duration of animpedance matching phase implemented with a device such as device 1 isthus significant.

A long impedance matching phase is not desirable, particularly whendevice 1 and the source of the sub-GHz RF signal belong to an electronicsystem powered by a battery. Indeed, during the impedance matchingphase, the source transmits the sub-GHz RF signal at the maximum powerthat it can supply so that the reflected power remains measurable by thedetector, even when the impedance of device 1 is matched with that ofthe source and this reflected power has a minimum value.

As a result, an impedance matching phase implemented with device 1 ishighly power-consuming. It would thus be desirable to be able todecrease the duration of the impedance matching phase, to decrease thepower consumption that it generates.

FIG. 2 shows, by means of a Smith chart, the impedance shifts thatdevice 1 is capable of correcting.

Smith charts are well known by those skilled in the art. A Smith chartparticularly enables to represent the impedance of a load, here, theimpedance of device 1, normalized with respect to a reference impedance,here, the impedance of the source of the sub-GHz RF signal. Theimpedance of device 1 normalized by that of the source is also callednormalized impedance of device 1. The center O if the chart correspondsto the case where the two impedances are equal, for example, to 50 ohms.

In a Smith chart, the set of decreased impedances belonging to a samecircle centered on center O of the chart correspond to a samecoefficient of reflection of a signal on the load, that is, in thisexample, to a same coefficient of reflection of a radiofrequency signalon device 1, the signal being supplied by the radiofrequency sourceconnected to the terminal 100 of device 1. When the coefficient isexpressed in dB, it is currently designated by initials RL, for ReturnLoss. The normalized impedances arranged inside of such a circlecorrespond to RL coefficients smaller than that of the normalizedimpedances arranged on the circle.

FIG. 2 shows a circle 200 corresponding to the normalized impedances ofdevice 1 for which the RL coefficient is equal to a threshold RLth,threshold RLth being preferably smaller than −5 dB, for example equal to−13 dB in this example. In the following description, it is, forexample, considered that the impedance of device 1 matches that of thesource delivering the sub-GHz RF signal to terminal 100 if thenormalized impedance of device 1 is arranged on or inside of circle 200,that is, if the normalized impedance corresponds to a RL coefficientsmaller than or equal to threshold RLth.

FIG. 2 shows, by an area A1 delimited by a full line, the set ofnormalized impedances device 1 which may be corrected by theimplementation of an impedance matching phase carried out in situ, thatis, which may be taken into circle 200 by appropriately modifying thevalues of the variable components of settable value of network 3 ofdevice 1. In other words, area A1 represents the set of impedancemismatches that device 1 is capable of correcting to recover animpedance which matches that of the source. In yet other words, area A1represents the set of normalized impedances that device 1 can take.

The inventors have observed that the impedance shifts of a device of thetype of device 1 caused by the environment of use of the device 1, thatis the environment where the device 1 is disposed to be used therein,result from the presence of a conductive element close to the device,for example, for example a metallic element, for example a pipe.

Further, when the impedance of device 1 matches that of source anddevice 1 undergoes an impedance mismatch caused by a conductive elementclose to the device, the normalized impedance of device 1 represented ina Smith chart is displaced from the center of the chart to the edge ofthe chart. The inventors have observed that this displacement of thenormalized impedance of device 1 approximatively follows a samedirection, shows by an arrow 202 in FIG. 2 , whatever the conductiveelement causing the mismatch is and whatever the position of theconductive element relative to device 1 is as soon as the conductiveelement is close enough to modify the impedance of device 1. In otherwords, the mismatches of impedance that device 1 having a givenconfiguration of network 3 and a given antenna 2 undergoes arepredictable as they follow this direction 202.

The inventors here provide taking advantage of the fact that theimpedance mismatches of a device of the type in FIG. 1 comprising agiven network 3 and a given antenna 2 are predictable. In particular,the inventors suggest to keep only one variable component of settablevalue in the impedance matching network of the device.

FIG. 3 shows in the form of a circuit an embodiment of an impedancematching device 1′.

Device 1′ is similar to the device 1 of FIG. 1 in that it comprisesantenna 2, terminal 100, and an impedance matching network 3′ couplingterminal 100 to antenna 2. The network 3′ of device 1′ is the singleimpedance matching network of device 1′.

Network 3′ comprises, like the network 3 described in relation with FIG.1 , inductive components, and/or capacitive components coupled togetherand to node 102. The inductive and/or capacitive components of network3′ couple an input terminal 304 of network 3′ to an output terminal 306of network 3′, terminals 304 and 306 being respectively coupled toterminal 100 and to antenna 2, terminal 306 being preferably connectedto antenna 2.

Network 3′ differs from network 3 in that it comprises a single variableinductive or capacitive component of settable value, the set of otherinductive and/or capacitive components of network 3′ having a fixedvalue.

According to an embodiment, the variable component of settable value isa capacitor, variable capacitors of settable capacitance value beingsimpler to implement than variable inductors of settable inductancevalue. In an alternative embodiment, that variable component of settablevalue could instead be an inductor.

According to an embodiment, the components of network 3′ are discretecomponents assembled on a printed circuit board.

In the example of FIG. 3 , network 3′ comprises a fixed capacitor C1′ offixed capacitance value connected between terminal 304 and node 102, afixed inductor L1 of fixed inductance value, and a fixed capacitor C2′of fixed capacitance value connected between terminals 304 and 306,inductor L1 being connected to terminal 304, and a fixed inductor L2 offixed inductance value and a variable capacitor C3 of settablecapacitance value connected in parallel between terminal 306 and node102.

The capacitance and inductance values of the fixed components of fixedvalue of network 3′ are determined so that the normalized impedance ofthe device 1′ submitted to an impedance mismatch caused by a conductiveelement close to the device 1′ belongs, in a Smith chart, to an areacorresponding to the set of possible capacitance or inductance values ofthe variable component of settable value of network 3′, this areacomprising to the center O of the chart. In other words, the capacitanceand inductance values of the fixed components of fixed value of thenetwork 3′ are determined so that the normalized impedance of device 1′submitted to an impedance mismatch caused by a conductive elementbelongs to the set of normalized impedances the device 1′ can take whenthe capacitance or inductance value of the variable component ofsettable value is modified. In yet other words, the values of thecomponents of fixed value of network 3′ are determined so that animpedance mismatch of device 1′ caused by a conductive element iscorrectable by a modification of the value of its variable component ofsettable capacitance or inductance value.

As an example, for a given network 3′ and a given antenna 2, thecapacitance and inductance values of the fixed components of fixed valueare determined by implementing, for example with a simulation tool, thefollowing successive steps:

-   -   1) select capacitance and inductance values of components of        network 3′ allowing to match the device 1′ impedance with that        of the source of the sub-GHz RF signal when device 1′ is in an        anechoic environment;    -   2) determine, for these selected capacitance and inductance        values, the set of the normalized impedances of device 1′        corresponding to the set of the possible capacitance or        inductance values of the variable component of settable value;    -   3) induce one or more impedance mismatches by a conductive        element and determine, for each of these impedance mismatches,        the normalized impedance of device 1′; and    -   4) verify if each normalized impedance determined at step 3) is        included in the set of the normalized impedances of device 1′        determined at step 2). In other words, step 4) comprises        verifying if the normalized impedance calculated at step 3)        belongs, in a Smith chart, to an area representing the set of        the normalized impedances taken by device 1′ when the whole        range of the possible capacitance or inductance value of the        variable component of settable value is scanned.

Steps 2) and 3) are repeated after having modified at least one of thevalues selected at step 1) and/or those of the network variablecomponents which has a settable value as long as each normalizedimpedance calculated at step 3) is outside the set of the normalizedimpedances calculated at step 2). When each normalized impedancecalculated at step 3) belongs to the set of the normalized impedancescalculated at step 2), the determination of the capacitance andinductance values of the fixed components of fixed value of the network3′ is finished. The determined capacitance and inductance values are theones used during the last implementation of the steps 2) and 3).

Those skilled in the art are capable of determining the capacitance andinductance values of the fixed components of fixed value of the networkin a different manner than that described above as an example.

Referring again to FIG. 2 , an area A2 delimited by dotted linesrepresents the set of normalized impedances of device 1′ whichcorrespond to the set of possible capacitance or inductance values ofthe variable component of settable value of network 3′. In FIG. 2 , thearea A2 is represented for the case where the capacitance and inductancevalues of the fixed components of fixed value of network 3′ have beendetermined indicated previously. Thus, when device 1′ undergoes animpedance mismatch caused by a conductive element of its environment,the normalized impedance of device 1′ moves in direction 202. When thenormalized impedance of device 1′ stays in the area A2, an appropriatemodification of the capacitance value of variable capacitor C3 enablesto take the normalized impedance of device 1′ into circle 200. In otherwords, when the normalized impedance of device 1′ having undergone animpedance mismatch stay in area A2, an impedance matching phase enablesto take the normalized impedance of device 1′ into circle 200, that isto say enable to readjust the impedance of device 1′ with that of thesource of the sub-GHz RF signal.

Due to the fact that the impedance matching network 3′ of device 1′comprises a single variable component of settable value, the duration ofan impedance matching phase implemented with device 1′ is shorter thanthat of an impedance matching phase implemented with a device of thetype of device 1 having its impedance matching network comprising atleast two variable components of settable value.

Further, due to the fact that network 3′ comprises a single variablecapacitor C3 of settable value, when the capacitance value of capacitorC3 is varied, the reflected power has a single minimum value, instead ofa plurality of local minimum values as in a device of the type of thedevice 1.

The inventors here provide taking advantage of the fact that there is asingle minimum reflected power when the value of variable capacitor C3varies to use a measurement circuit or detector less sensitive thanthose necessary for the implementation of an impedance matching phase ina device of the type of that of FIG. 1 .

Indeed, in a device of the type of the device 1, as there are aplurality of local minimums of the reflected power, it is necessary toknow the values of these local minimums to determine which of theselocal minimums corresponds to the lowest reflected power. The impedancematching is then made by controlling the capacitance or inductancevalues of the variable components of settable value of the network 3 sothat their values are those corresponding to the local minimum for whichthe reflected power is the lowest. On the contrary, in device 1′, asthere is only one minimum of the reflected power, it is not necessary toprecisely known the corresponding value of the reflected power.

According to an embodiment, as illustrated in FIG. 3 , the detector ofdevice 1′ comprises a directional coupler 4. Coupler 4 comprises a port401 configured to be connected to the source of a sub-GHz RF signal,port 401 being coupled, preferably connected, to terminal 100. Coupler 4further comprises a port 402. Coupler 4 is configured to transmit toport 402 a sub-GHz RF signal received by its port 401. Port 402 iscoupled, preferably connected, to the terminal 304 of network 3′.Coupler 4 further comprises a port 403. Coupler 4 is configured totransmit the sub-GHz RF signal received by its port 402 to port 403. Thesub-GHz RF signal received by port 402 corresponds to the sub-GHz RFsignal reflected by the assembly of network 3′ and of antenna 2, thereflected signal propagating towards terminal 100. The signal on port403 corresponds, in practice, to an attenuated version of the signalreceived by the port 402. This attenuation results from the couplinglosses between ports 402 and 403, and is, for example, in the order of20 dB.

In the example of FIG. 3 , coupler 4 further comprises a port 404,towards which an attenuated version of the signal received by port 401is transmitted. This attenuation results from the coupling lossesbetween ports 401 and 404, and is, for example, equal to that betweenport 402 and 403. A resistor 5 is connected between ports 404 and node102 to match the impedance viewed by port 404 to that of port 404 ofcoupler 4, which is, in practice, equal to that of the source of thesub-GHz RF signal.

According to another example, not shown, coupler 4 does not compriseport 404 and the resistor 5 then forms part of coupler 4.

According to an embodiment where the components of network 3′ arediscrete components assembled on a printed circuit board, coupler 4 is adiscrete component assembled on the same printed circuit board.

The detector of device 1′ further comprises a diode 6 coupling port 403to a measurement terminal 104 of device 1′. An electrode of diode 6, itsanode, is coupled, preferably connected, to port 403, the otherelectrode of diode 6, its cathode, is coupled, preferably connected, toterminal 104.

Diode 6 is configured to rectify the sub-GHz RF signal present on port403 and to deliver a corresponding rectified voltage Vmes to terminal104.

According to an embodiment where the components of network 3′ arediscrete components assembled on a printed circuit board, diode 6 is,preferably, a discrete component assembled on the same printed circuitboard.

The detector of device 1′ further comprises a low-pass filter 7connected to terminal 104. The filter 7 is configured to smooth therectified voltage Vmes present on terminal 104, so that voltage Vmes 104is a DC voltage. In the example, the low-pass filter 7 comprises acapacitor 701 connected between terminal 104 and node 102, and aresistor 702 connected between terminal 104 and node 702, in parallelwith the capacitor 701. The value of the resistor 702 is chosen to makethe impedance viewed by port 104 equal to that of port 403 of coupler 4.

According to an embodiment where the components of network 3′ arediscrete components assembled on the printed circuit board, filter 7 ispreferably formed of one or a plurality of discrete components assembledon the same printed circuit board.

Voltage Vmes is representative of the reflected power. Moreparticularly, the higher, respectively the lower, value of voltage Vmesis, the higher, respectively the lower, the reflected power, voltageVmes being minimal when the reflected power is minimal, that is to saywhen the impedance of the device 1′ matches that of the radiofrequencysource connected to terminal 100.

Measurement terminal 104 is configured to be connected to ananalog-to-digital converter (ADC) that is not shown in FIG. 4 . The ADC,when it is connected to terminal 104, forms part of the detector ofdevice 1′. The ADC is configured to deliver a signal or digital codeover a plurality of bits, the digital code being representative of thevalue of voltage Vmes, and thus of that of the reflected power.

The ADC comprises a conversion range delimited by a maximum voltage Vmaxand a minimum voltage Vmin. If the voltage Vmes on terminal 104 has avalue greater than or equal to voltage Vmax, the ADC will indicate thatthe measured voltage Vmes is equal to voltage Vmax. If the voltage Vmeson terminal 104 has a value smaller than or equal to voltage Vmin, theADC will indicate that the measured value Vmes is equal to voltage Vmin.Voltage Vmin determines the maximum sensitivity of the detector, thatis, the minimum power of the signal delivered by port 403 to thedetector which results in a voltage Vmes on terminal 104 in theconversion range of the ADC.

During an impedance matching phase carried out in situ, voltage Vmes isgreater than voltage Vmin as long as the coefficient RL is greater thana threshold RLlim (in dB) determined by relation RLlim=Ds+C−Pi, Ds beingthe maximum sensitivity of the detector in dBm, Pi being the power ofthe signal delivered to terminal 100 in dBm, and C representing thecoupling losses between ports 402 and 403 in dB.

As an example, threshold RLlim is equal to −13 dB when power Pi is equalto 10 dBm, the coupling losses C are equal to 20 dB, and the maximumsensitivity Ds is equal to −23 dBm.

According to an embodiment, the ADC of device 1′ belongs to amicrocontroller (not shown) configured to implement an impedancematching phase by use of device 1′. Preferably, the microcontrollercomprises a digital-to-analog converter or DAC, configured to controlthe variable component of settable value (for example, capacitor C3) ofnetwork 3′. Preferably, the microcontroller also comprises amicroprocessor receiving data from the ADC and supplying data to the DACto control the setting of the capacitance and inductance value of thevariable component.

FIG. 4 illustrates, in the form of a flowchart, an embodiment of amethod of use of device 1′. This method of use corresponds, in practice,to a method for matching in situ the impedance of device 1′ with that ofthe radiofrequency source connected to the terminal 101 of device 1′.

In that method, the capacitance or inductance value of the variablecomponent is varied and the voltage Vmes is measured for each valuetaken by the variable component as long as the measured voltage Vmes isdecreasing or constant, and the variation of the variable componentvalue is stopped as soon as the measured voltage Vmes is strictlyincreasing. This makes it possible to measure the voltage Vmes over onlypart of the range of possible values of the variable component, whichmakes it possible to reduce the time necessary for the implementation ofthe method. We take advantage here of the fact that the reflected powerhas only one minimum when the value of the variable component varies.

At a step 900 (block “START”), an initial capacitance value Cinit of thevariable capacitor C3 is selected. As an example, the value Cinit is thecurrent value of the variable capacitor C3 at the beginning of themethod, its maximum value Cmax or its minimal value Cmin, preferably itscurrent value. At step 900, the capacitance and inductance values of thefixed components of fixed value of network 3′ have been (beforehand) setas previously described, and the assembly of the device 1′ and of theradiofrequency source connected to the terminal 100 (FIG. 3 ) is in itsenvironment of use. In practice, device 1′ then forms part of anelectronic system comprising the ADC connected to terminal 104 and acircuit for controlling the variable component of settable value ofnetwork 3′.

At a next step 902 (block “SET ORDER”), a scanning direction, orscrolling direction, of the capacitance values of the variable capacitorC3 from the value Cinit is determined among the increasing direction andthe decreasing direction. More particularly, the increasing ordecreasing order of the successive capacitance values of the variablecapacitor C3 is determined so that, during the following steps of themethod, at least the first two measured values of the voltage Vmes aredecreasing, or, in other words, are not strictly increasing.

The implementation of this step is in the abilities of those skilled inthe art, for example by selecting a scanning direction, by measuring,for this scanning direction, voltage Vmes for at least the first twosuccessive capacitance values of the variable capacitor C3, by verifyingif the selected scanning direction corresponds to a decreasing measuredvoltage Vmes, and by modifying the scanning direction if needed.

At a next step 904 (block “MEASURE”), the voltage Vmes on the terminal104 is measured for the Cinit value of the variable capacitor C3. Itwill be noted that, if the previous step 902 includes a measurement ofthe voltage Vmes on the terminal 104 for the Cinit value, this step 904can be omitted.

At a next step 906 (block “CHANGE VAL”), the capacitance value ofvariable capacitor C3 is modified while respecting the scanningdirection fixed at step 902.

At a next step 908 (block “MEASURE”), the voltage Vmes on terminal 104is measured for the current capacitance value of variable capacitor C3.

At a next step 910 (block “LAST MEASURE>BEFORE LAST MEASURE”), it isverified whether the last measured voltage Vmes is strictly greater thanthe penultimate measured voltage Vmes. We call here “measured voltageVmes” the measurement or value of the voltage Vmes which is supplied bythe ADC connected to terminal 104. A measured voltage Vmes maycorrespond to a value different from that of the voltage Vmes actuallypresent on the terminal 104, typically when the voltage Vmes on terminal104 is outside the ADC conversion range.

If the last voltage Vmes measured is not strictly greater than thepenultimate voltage Vmes measured (branch N of block 910), the methodcontinues at step 912 (block “VAL=VALmin or VALmax”). If the lastmeasured voltage Vmes is strictly greater than the penultimate measuredvoltage Vmes (branch Y of block 910), the method continues at a step 914(block “END”).

At step 912, it is verified whether the current capacitance value of thevariable capacitor C3 is equal to its maximum value Cmax or to itsminimum value Cmin. More particularly, if the capacitance values ofvariable capacitor C3 are scanned in the increasing order, it is checkedwhether the current capacitance value of variable capacitor C3 is equalto its maximum value Cmax, and, if the capacitance values of variablecapacitor C3 are scanned in the decreasing order, it is checked whetherthe current capacitance value of variable capacitor C3 is equal to itsminimum value Cmin.

If this is the case (branch Y of block 912), the method continues atstep 914. If this is not the case (branch N of block 912), the processcontinues at step 906.

Step 914 comprises selecting a capacitance value of the variablecapacitor C3 making it possible to adapt the impedance of the device 1′to that of the source of the sub-GHz RF signal. Variable capacitor C3 isthen controlled so that it takes the selected capacitance value. Forthis, a set of capacitance values of the variable capacitor C3corresponding to the minimum measured voltage Vmes is determined fromamong all the capacitance values taken by the variable capacitor C3during the preceding steps, then a capacitance value of the variablecapacitor C3 is selected from this set.

The implementation of the method described in relation with FIG. 4allows for adapting the impedance of the device 1′ to that of the sourceof the sub-GHz RF signal.

Indeed, in the case where the set determined in step 914 comprisesseveral capacitance values of variable capacitor C3, these capacitancevalues all correspond to voltages Vmes measured equal to the voltageVmin. In other words, these values all correspond to a voltage Vmes onterminal 104 smaller than the voltage Vmin of the ADC. These capacitancevalues of capacitor C3 therefore all correspond to a coefficient RLsmaller than the threshold RLlim.

Further, in the case where the set determined in step 914 includes onlyone capacitance value, this means that the voltage Vmes corresponding tothis capacitance value of the variable capacitor C3 is minimum, andtherefore corresponds to a minimum reflected power for the considereddevice 1′. This case occurs when the voltage Vmes has a minimum valuegreater than the voltage Vmin of the ADC, that is to say that thecoefficient RL remains above threshold RLlim regardless of thecapacitance value of the variable capacitor C3. Even in this case, themethod described above makes it possible to minimize the power reflectedfor the device 1′ as well as possible, and therefore to adapt theimpedance of the device 1′ to that of the source of the sub-GHz RFsignal. This case corresponds for example to an impedance mismatch forwhich the normalized impedance of the device 1′ does not belong to thearea A2 (FIG. 2 ).

According to one embodiment, the variable component of settablecapacitance or inductance value is controlled so that its capacitance orinductance value is equal to a median value of the set determined instep 914. By median value here is meant a value of the set for which theset includes as many values below the median value as there are valuesabove, to within one value.

According to one embodiment, the method is implemented following arequest from a user of the device 1′ and/or periodically.

According to one embodiment, the method described above is implementedby a microcontroller comprising the ADC which is connected to theterminal 104 of the device 1′ and a control circuit of the variablecapacitor C3, for example a DAC. The microcontroller includes amicroprocessor or processing unit associated with a memory comprisinginstructions which, when read by the microprocessor of themicrocontroller, cause the implementation of the method.

It will be noted that although the implementation of FIG. 3 ′ shows useof a single variable component as a variable capacitor, the singlecomponent could instead be one of the inductors. The process describedabove is equally applicable in the case where the variable component isan inductor and the operation is to determine the inductance value whichadapts the impedance of the device 1′ to that of the source of thesub-GHz RF signal.

Examples of implementations of the method of FIG. 4 will now bedescribed in relation to FIGS. 5, 6 and 7 .

FIG. 5 illustrates an example of implementation of the method describedin relation to FIG. 4 . The example of FIG. 5 corresponds to the casewhere, over the whole range of possible capacitance values of variablecapacitor C3, the voltage Vmes on terminal 104 decreases to a minimumvalue and then increases from this minimum value, and where the minimumvalue of the voltage Vmes on terminal 104 is smaller than the minimumvoltage Vmin of the ADC.

A curve 1000 represents the evolution of the voltage Vmes on theterminal 104 as a function of the capacitance value of the variablecapacitor C3 of the network 3′. A horizontal axis 1002 represents thevoltage Vmin of the ADC connected to the measurement terminal 104 of thedevice 1′. Points 1003 represent the voltages Vmes measured by thedetector of the device 1′, that is to say the measurements of thevoltage Vmes supplied by the ADC. In FIG. 5 , in order not to overloadthe figure, a reduced number of points are shown and only two of thesepoints 1003 are referenced. Each point 1003 is obtained for acorresponding capacitance value of the variable capacitor C3 takenduring the implementation of the method.

The capacitance value Cinit of the variable capacitor C3 is, in thisexample, the current capacitance value of the variable capacitor C3 atthe start of the method (step 900, FIG. 4 ), and the capacitance valuesof the variable capacitor C3 are scanned in the increasing direction(step 902, Figure. 4 ).

Several measurements of the voltage Vmes (steps 904, FIG. 4 ) are thencarried out by modifying, between each two successive measurements, thecapacitance value of the variable capacitor C3 (steps 906, FIG. 4 ).

Up to a capacitance value val2 of the variable capacitor C3, eachmeasured voltage Vmes is smaller than the previous measured voltage Vmes(step 910, branch N, FIG. 4 ).

More particularly, in this example, each measurement of the voltage Vmesis strictly smaller than the previous measurement of the voltage Vmesfor the successively increasing capacitance values of the variablecapacitor C3 ranging from the value Cinit to a value val1, and is equalto the previous measurement of the voltage Vmes for the successivelyincreasing capacitance values of the variable capacitor C3 going fromthe value val1 to the value val2.

On the other hand, when the variable capacitor C3 changes to acapacitance value val3 following the capacitance value val2 (step 906,FIG. 4 ), the measured voltage Vmes for the value val3 (step 908, FIG. 4) is strictly greater than the measured voltage Vmes for the value val2(step 910, branch Y, FIG. 4 ). As a result, the modifications of thecapacitance value of variable capacitor C3 and the measurement of thevoltage Vmes for each capacitance value of variable capacitor C3 arestopped, without having scanned all the capacitance values of variablecapacitor C3. This makes it possible to reduce the duration ofimplementation of the method compared to that of a method in which allthe capacitance values of the variable capacitor C3 would have beenscanned.

Among all the successive capacitance values taken by the variablecapacitor C3, the set of capacitance values corresponding to a minimummeasured voltage Vmes is then determined (step 914, FIG. 4 ). In thisexample, this set includes all the capacitance values of the variablecapacitor C3 going from the capacitance value val1 to the capacitancevalue val2, which all correspond to a voltage Vmes on the terminal 104smaller than the voltage Vmin, therefore to coefficients RL smaller thanthe threshold RLlim. A capacitance value val4 of the variable capacitorC3 is then selected from this set, and the variable capacitor C3 iscontrolled so that its capacitance value is equal to the selectedcapacitance value.

Preferably, the capacitance value val4 is the median capacitance valueof the set. This makes it possible, in the case of FIG. 5 , to be closerto the minimum reflected power than if the capacitance value val4 hadbeen selected randomly in the set.

FIG. 6 illustrates another example of implementation of the methoddescribed in relation to FIG. 4 . The example of FIG. 6 corresponds tothe case where, over the whole range of possible capacitance values ofvariable capacitor C3, the voltage Vmes is only decreasing when thecapacitance values of variable capacitor C3 are scanned in increasingorder, and where the voltage Vmes on terminal 104 takes values smallerthan the minimum voltage Vmin of the ADC.

A curve 1004 represents the evolution of the voltage Vmes on theterminal 104 as a function of the capacitance value of the variablecapacitor C3 of the network 3′. As in FIG. 5 , the axis 1002 representsthe voltage Vmin and points 1003 represent the voltages Vmes measured bythe detector of the device 1′, the number of represented points and thenumber of referenced points being reduced so as not to overload thefigure. Each point 1003 is obtained for a corresponding capacitancevalue of the variable capacitor C3 taken during the implementation ofthe method.

In this example, the capacitance value Cinit of variable capacitor C3 isthe current capacitance value of variable capacitor C3 at the start ofthe method (step 900, FIG. 4 ), and the capacitance values of variablecapacitor C3 are scanned in increasing order (step 902, FIG. 4 ).

Several measurements of the voltage Vmes (steps 904, FIG. 4 ) arecarried out by modifying, between each two successive measurements, thecapacitance value of the variable capacitor C3 (steps 906, FIG. 4 ).

Up to the capacitance value Cmax, each measured voltage Vmes is smallerthan or equal to the previous measured the voltage Vmes (step 910,branch N, FIG. 4 ).

More particularly, in this example, each measurement of the voltage Vmesis strictly smaller than the previous measurement of the voltage Vmesfor the capacitance values of the variable capacitor C3 ranging from theCinit value to a capacitance value val5, and is equal to the previousmeasurement of the voltage Vmes for the capacitance values of thevariable capacitor C3 ranging from the capacitance value val5 to thevalue Cmax.

The set of capacitance values corresponding to a minimum measuredvoltage Vmes (step 914, FIG. 4 ) is then determined. In this example,this set includes all the capacitance values of the variable capacitorC3 ranging from the capacitance value val5 to the value Cmax, which allcorrespond to a voltage Vmes on the terminal 104 smaller than thevoltage Vmin, therefore to coefficients RL smaller than the thresholdRLlim.

A capacitance value val6 of the variable capacitor C3 is then selectedfrom this set of capacitance values of the variable capacitor C3, andthe variable capacitor C3 is controlled so that its capacitance value isequal to the selected capacitance value.

FIG. 7 illustrates yet another example of implementation of the methoddescribed in relation to FIG. 4 . The example of FIG. 7 corresponds tothe case where, over the whole range of possible capacitance values ofvariable capacitor C3, the voltage Vmes on terminal 104 decreases to aminimum value then increases from this minimum value, and where theminimum voltage Vmes on terminal 104 is greater than the voltage Vmin ofthe ADC.

A curve 1006 represents the evolution of the voltage Vmes on theterminal 104 as a function of the capacitance value of the variablecapacitor C3 of the network 3′. The horizontal axis 1002 represents thevoltage Vmin. Points 1003 represent the voltages Vmes measured by thedetector of the device 1′, the number of represented points and thenumber of referenced points being reduced so as not to overload thefigure. Each point 1003 is obtained for a corresponding capacitancevalue of the variable capacitor C3 taken during the implementation ofthe method.

In this example, the capacitance value Cinit of the variable capacitorC3 is the current capacitance value of the variable capacitor C3 at thestart of the process (step 900, FIG. 4 ), and the capacitance values ofthe variable capacitor C3 are scanned in the increasing direction (step902, FIG. 4 ).

Several measurements of the voltage Vmes (steps 904, FIG. 4 ) arecarried out by modifying, between each two successive measurements, thecapacitance value of the variable capacitor C3 (steps 906, FIG. 4 ).

Up to a capacitance value val7, each measured voltage Vmes is strictlysmaller than the previous measured voltage Vmes (step 910, branch N,FIG. 4 ). On the other hand, when the variable capacitor C3 takes acapacitance value val8 following the value val7 (step 906, FIG. 4 ), themeasurement of the voltage Vmes corresponding to the capacitance valueval8 (step 908, FIG. 4 ) is strictly greater than the previousmeasurement of the voltage Vmes corresponding to the capacitance valueval7 (step 910, branch Y, FIG. 4 ). As a result, the modifications ofthe capacitance value of variable capacitor C3 and the measurement ofthe voltage Vmes for each capacitance value of variable capacitor C3 arestopped, without having scanned all the capacitance values of variablecapacitor C3. This makes it possible to reduce the duration ofimplementation of the method compared to that of a method in which allthe capacitance values of the variable capacitor C3 would have beenscanned.

The set of capacitance values corresponding to a minimum measurement ofthe voltage Vmes (step 914, FIG. 4 ) here only includes the capacitancevalue val7. The variable capacitor C3 is then controlled so that itscapacitance value is equal to this single capacitance value val7 of theset.

Embodiments and variants for which threshold RLlim is equal to −13 dB,have been described hereabove. It will be within the abilities of thoseskilled in the art to modify the value of threshold RLlim. For example,the value of threshold RLlim may be decreased by providing to increasepower Pi to respect RLlim=Ds+C−Pi, coupling losses C and the sensitivityDs of the detector being intrinsic characteristics of device 1′ whichdepend on the coupler 4 and on the ADC used.

Various embodiments and variants have been described. Those skilled inthe art will understand that certain features of these variousembodiments and variants may be combined, and other variants will occurto those skilled in the art. In particular, the implementation ofnetwork 3′ is not limited to the example shown in FIG. 3 , and it willbe within the abilities of those skilled in the art to provide otherexamples of networks 3′ comprising a plurality of inductive and/orcapacitive components, including a single variable component of settable(capacitance or inductance) value, and will know how to implement themethod described in relation with FIG. 4 for these other examples.

Finally, the practical implementation of the described embodiments andvariations is within the abilities of those skilled in the art based onthe functional indications given hereabove. In particular, those skilledin the art will know how to vary the value of the adjustable valuecomponent, for example with a constant step. As an example, when thecomponent is controlled by an output voltage of a digital to analogconverter, this constant step is for example determined by the variationof the output voltage of the converter between two successive binarycodes supplied at the input of the converter.

1. A method for determining an inductance or capacitance value of avariable component within an impedance matching network comprising aplurality of fixed components having fixed inductance and capacitancevalues and said variable component having a variable inductance orcapacitance value, comprising: a) selecting an initial inductance orcapacitance value of the variable component and obtaining a measurementof a voltage indicative of power of a reflected signal received by saidimpedance matching network; and b) changing the inductance orcapacitance value of the variable component in a determined scanningdirection and obtaining a further measurement of the voltage indicativeof power of the reflected signal; wherein step b) is repeated until saidfurther measured voltage is strictly greater than a penultimatelyobtained measurement of the voltage indicative of power of the reflectedsignal.
 2. The method according to claim 1, further comprising, afterstep b): c) determining a set comprising each inductance or capacitancevalue of the variable component corresponding to a minimal voltagemeasurement; and d) controlling the variable component to set itsinductance or capacitance value to belong to said set.
 3. The methodaccording to claim 2, wherein steps a), b) and c) are implemented in aperiodic manner.
 4. The method according to claim 2, wherein steps a),b) and c) are implemented in response to a user request.
 5. The methodaccording to claim 1, further comprising, after step b): c) determininga set comprising each inductance or capacitance value of the variablecomponent corresponding to a minimal voltage measurement; and d)controlling the variable component to set its inductance or capacitancevalue at a median value of said set.
 6. The method according to claim 5,wherein steps a), b) and c) are implemented in a periodic manner.
 7. Themethod according to claim 5, wherein steps a), b) and c) are implementedin response to a user request.
 8. The method according to claim 1,further comprising, prior to step a): determining inductance andcapacitance values of the fixed components so that a normalizedimpedance after an impedance mismatch caused by presence of a proximateconductive element belongs to an area in a Smith chart determined by allinductance or capacitance values of the variable component.
 9. Themethod according to claim 8, wherein determining comprises: 1)determining inductance and capacitance values of the fixed componentsfor which an impedance matches that of a source of a radiofrequencysignal applied to the impedance matching network in an anechoicenvironment; 2) calculating a normalized impedance for each inductanceor capacitance value of the variable component; 3) proximately disposinga conductive element and calculating a further normalized impedance; and4) repeating steps 2) and 3) with a modification of at least one of theinductance and capacitance values selected at step 1) as long as thefurther normalized impedance calculated at step 3) is outside a setcomprising all the normalized impedance calculated at step 2).
 10. Themethod according to claim 8, wherein determining comprises: 1)determining inductance and capacitance values of the fixed componentsfor which an impedance matches that of a source of a radiofrequencysignal applied to the impedance matching network in an anechoicenvironment; 2) calculating a normalized impedance for each inductanceor capacitance values of the variable component; 3) proximatelydisposing a conductive element and calculating a further normalizedimpedance; and 4) repeating steps 2) and 3) with a modification of theinductance or capacitance value of the variable component as long as thefurther normalized impedance calculated at step 3) is outside a setcomprising all the normalized impedance calculated at step 2).
 11. Themethod according to claim 1, wherein the variable component is acapacitor.
 12. The method according to claim 1, wherein the variablecomponent is the only component in the impedance matching network whichvariable.
 13. A method for determining an inductance or capacitancevalue of a variable component within an impedance matching networkcomprising a plurality of fixed components having fixed inductance andcapacitance values and said variable component having a variableinductance or capacitance value, comprising: a) selecting an initialinductance or capacitance value of the variable component and obtaininga measurement of a voltage indicative of power of a reflected signalreceived by said impedance matching network; b) changing the inductanceor capacitance value of the variable component in a determined scanningdirection and obtaining a further measurement of the voltage indicativeof power of the reflected signal; and c) repeating step b) until aminimal of the voltage indicative of power of the reflected signal isdetected.
 14. The method according to claim 13, further comprising:determining a set of inductance or capacitance values of the variablecomponent which are adjacent the detected minimal of the voltageindicative of power of the reflected signal; and setting an inductanceor capacitance value of the variable component to one of the inductanceor capacitance values belonging to said set.
 15. The method according toclaim 13, further comprising: determining a set of inductance orcapacitance values of the variable component which are adjacent thedetected minimal of the voltage indicative of power of the reflectedsignal; and setting an inductance or capacitance value of the variablecomponent to equal a median of the inductance or capacitance valuesbelonging to said set.
 16. The method according to claim 13, furthercomprising, prior to step a): determining inductance and capacitancevalues of the fixed components so that a normalized impedance after animpedance mismatch caused by presence of a proximate conductive elementbelongs to an area in a Smith chart determined by all inductance orcapacitance values of the variable component.
 17. The method accordingto claim 16, wherein determining comprises: 1) determining inductanceand capacitance values of the fixed components for which an impedancematches that of a source of a radiofrequency signal applied to theimpedance matching network in an anechoic environment; 2) calculating anormalized impedance for each inductance or capacitance value of thevariable component; 3) proximately disposing a conductive element andcalculating a further normalized impedance; and 4) repeating steps 2)and 3) with a modification of at least one of the inductance andcapacitance values selected at step 1) as long as the further normalizedimpedance calculated at step 3) is outside a set comprising all thenormalized impedance calculated at step 2).
 18. The method according toclaim 16, wherein determining comprises: 1) determining inductance andcapacitance values of the fixed components for which an impedancematches that of a source of a radiofrequency signal applied to theimpedance matching network in an anechoic environment; 2) calculating anormalized impedance for each inductance or capacitance values of thevariable component; 3) proximately disposing a conductive element andcalculating a further normalized impedance; and 4) repeating steps 2)and 3) with a modification of the inductance or capacitance value of thevariable component as long as the further normalized impedancecalculated at step 3) is outside a set comprising all the normalizedimpedance calculated at step 2).
 19. The method according to claim 13,wherein the variable component is a capacitor.
 20. The method accordingto claim 13, wherein the variable component is the only component in theimpedance matching network which variable.